I'm confused. Does your Colt 6920 not have a flash hider on it? If so, it should already have a threaded barrel.

You can get a Living Trust, and anyone in the trust can pick up a new suppressor from the shop when the Form 4 comes back. You can also look at the silencer forums and see if someone local has a silencer to sell, but it would still require a 6 month wait for the Form 4 to come back before you could get it. Personally, I prefer having my stuff in a dealer's inventory for 6 months rather than in an individual's posession. Unless I know that individual very well.